We propose a new optical sensing method that enables real-time, ultra-fast, and extremely sensitive detection and imaging of single cardiac troponin-T (cTnT) molecules in complex biological samples like human blood serum. By combining an expanded laser excitation spot with fluorescent labeling strategies optimized for high photon collection, we overcome the limitations of traditional single-molecule fluorescence detection. The technique achieves detection that is about 1000 times faster than existing approaches, while still maintaining the ability to directly image single cTnT molecules and measure their concentration with clinical-relevant sensitivity (~1 pg/mL). This approach could be extended to monitoring other biomolecules, viruses, or bacteria at the single-particle level in real time.
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